Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen portion thereof with a graphical user interface showing our new design;

FIG. 2 is a front view of a second embodiment thereof;

FIG. 3 is a front view of a third embodiment thereof;

FIG. 4 is a front view of a fourth embodiment thereof;

FIG. 5 is a front view of a fifth embodiment thereof; and,

FIG. 6 is a front view of a sixth embodiment thereof.

The broken line showing of display screens, portions of display screen, text and graphical elements form no part the claimed design. 

The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 